Rohit Gupta wrote:
Hi,
What is it in L2TP that i cant do with a simple GRE tunneling when implementing
a remote access
VPN for a mobile client to connect to the corporate network. In L2TP, since it
uses PPP
end-to-end, the LNS is able to supply dynamic IP address using IPCP to the
remote client. LNS
takes this IP address from a pool of IP addresses it has. If one were to use
GRE, then the same
can be done by using some out-of-band mechanism (or even have a fixed IP
address which the mobile
client is instructed to use). GRE will tunnel the data packet originated from
the mobile client,
the inner IP header will have the ip addresses as assigned by the corporate
network. The outer IP
header will contain the IP address of teh ISP and the gateway to reach the
corporate network.
GRE is an encapsulation. If you can manually provision or have some other "out
of band" mechanism that does everything L2TP and PPP would otherwise do for you,
then by all means use GRE - or IP in IP for that matter as your scenario with
fixed IP addresses for all mobile clients (which I would think is a showstopper
from the start) does not obviate the need for a GRE shim either.
L2TP is an encapsulation that allows multiplexing of multiple PPP sessions
between two IP-connected endpoints, and a control protocol for dynamically
establishing and maintaining the emulation of these PPP sessions. This is very
different than GRE (though there are some ways to deploy L2TP between two
routers to make it look like it is doing what GRE typically does in a bit more
of a dynamic manner, though this is really a subset of L2TP's overall
functionality).
Since you indicate that this is for a mobile environment, you might want to look
at using Mobile IP.
My whole point is that i want to know as to what is the burning need to have
L2TP!
This question probably has more to do with whether you need PPP. If you do, L2TP
could work for you to transport that PPP session (or many PPP sessions) over an
IP network. If not, I see no reason for you to be burning with need for L2TP!
- Mark
Regards,
Rohit
P.S.
Am not sure if this is indeed the right place to ask this question. But since
there will be a lot
of experienced people on this list who would have worked on both these
protocols, replying to this
one should be very easy.
__________________________________
Do you Yahoo!?
Yahoo! Mail - More reliable, more storage, less spam
http://mail.yahoo.com